1. Field of the Invention
The present invention relates to a signal selecting circuit and a recording medium having a program recorded thereon.
2. Description of the Related Art
In recent car audio systems, music or voices from different sound sources have come to be outputted separately to front speakers and rear speakers (see, e.g., Japanese Patent Application Laid-open Publication No. 2005-223505). In such car audio systems, an analog selector has often been used for selecting sound sources to be outputted separately to the front speakers and the rear speakers from among a plurality of sound sources (analogue signals) such as a CD, an MD, and a radio.
FIG. 14 depicts a common example of the configuration of the analog selector for selecting sound sources to be outputted separately to the front speakers and the rear speakers. An analog selector 201 serves to select a sound source outputted to the front speakers and includes switches 211 and 212, resistors 213 to 215, and an operational amplifier 216. An analog selector 221 serves to select a sound source outputted to the rear speakers and includes switches 231 and 232, resistors 233 to 235, and an operational amplifier 236. Input signals A and B are fed as selectable sound sources to each of the analog selectors 201 and 221. For example, by turning the switch 211 on and the switch 212 off, the switch 231 off, and the switch 232 on, the input signal A is provided as output (analog output 1) to the front speakers and the output signal B is provided as output (analog output 2) to the rear speakers.
In this manner, use of the analog selectors 201 and 221 enables music or voices from different sound sources to be outputted separately to the front speakers and the rear speakers.
In the configuration of FIG. 14, however, when the same sound source as being selected by one of the front and the rear is selected by the other, the one not changing the sound source undergoes occurrence of a switching noise. Assume for example that the switches 211, 212, 231, and 232 are on, off, off, and on, respectively, so that the input signals A and B are provided as the analog outputs 1 and 2, respectively. It is further assumed that the switches 231 and 232 are turned on and off, respectively, to switch the signal provided as the analog output 2 to the input signal A provided as the analog output 1. At that time, a switching noise occurs due to the switch 231 on and propagates to the switch 211. Therefore, when the rear selects the same sound source as the front does, a nose will occur in the analog output 1 provided to the front speakers though the front does not change the sound source. Similarly, when the front selects the same sound source as the rear does, a nose will occur in the analog output 2 provided to the rear speakers though the rear does not change the sound source.